The brain includes gray matter, primarily collections of neurons which serve to process information and generate responsive signals, and white matter, primarily axons which serve to communicate these signals between gray matter regions and more distant parts of the nervous system. It is well known that specific regions within the gray matter are associated with particular functions; for example, motor skills are primarily controlled by regions in the cerebral cortex, the cerebellum, and the basal ganglia. Thus, there is significant interest in measuring and interpreting signals from, and delivering signals to, different regions of the brain to allow the brain to communicate with external devices and/or to modify the brain's activity. As an example, in the developing field of DBS (Deep Brain Stimulation), people with motor disorders such as Parkinson's Disease may be able to experience a significant decrease (or even cessation) of muscle tremors by the use of signals delivered to the brain (more specifically to the basal ganglia). As another example, in the developing field of man-machine interfaces, electrode arrays are implanted in the brain and the signals measured therefrom may be used to control prostheses, communication devices, or other machines. Further details can be found, for example, in U.S. Pat. No. 6,066,163 to John, U.S. Pat. No. 6,354,299 to Fischell et al., U.S. Pat. No. 6,459,936 to Fischell et al., U.S. Pat. No. 6,463,328 to John, U.S. Pat. No. 6,484,059 to Gielen, U.S. Pat. No. 6,539,263 to Schiff et al., U.S. Pat. No. 6,662,035 to Sochor, U.S. Pat. No. 6,587,724 to Mann, and U.S. Pat. No. 6,731,986 to Mann.
However, several difficulties are encountered when attempting to communicate signals to or from a particular functional region of the brain (or to some subregion thereof). One significant problem relates to proper electrode placement: how does one know whether the electrode is situated at the proper region in the brain—the one related to a particular functionality, or which communicates particular signals? Or, looking at this question conversely, if an electrode is situated at a desired region in the brain, how does one determine what signal might best be delivered to this region—in other words, what is the general “communications protocol” used by this region (the signature of the electrical pulses used by the neurons therein)? Further details can be found, for example, in U.S. Pat. No. 6,011,996 to Gielen et al., U.S. Pat. No. 6,253,109 to Gielen, U.S. Pat. No. 6,301,492 to Zonenshayn, U.S. Pat. No. 6,606,521 to Paspa et al., 6,330,466 to Hofmann et al., U.S. Pat. No. 6,657,690 to Giller et al., and U.S. Pat. No. 6,694,162 to Hartlep.